Ohhhhhhh...it's a stopper/holder for the shelves in your cabinet lah....u ever notice the little little holes at the side of the cabinet where u can adjust the height of each shelves? That's the purpose lorr..

Poke the thing into the hole of your desired height and place the piece of plywood on top of it.... U need at least 2 to hold them, ok??

Better return this piece to the rightful owner?? How to detect, just look for a slanting shelves!!!